O-_Cu2+_O- (S=3/2) Formation in (CeO2)0.75(La2CuO4)0.25 Catalyst, during reduction of NO by CO

During an investigation on the properties of La(1-x)Ce(x)CuO(4) as catalyst for NO reduction by CO, samples with x = 0, 0.05, 0.10, 0.15, and 0.20 have been examinedAll of them showed a weak EPR line attributable to Cu2+ isolated ions. Furthermore, after use as catalyst for NO reduction by CO, the sample with x = 0.2 showed also an unusual EPR line at a field value ranging between about 1200 and 2700 G, when changing temperature from 150 K up to 400 K. Then, samples by far reacher in oxygen were produced by a different procedure and examined as catalysts for NO reduction by CO. A detaild analysis of the EPR spectra allowed us to hypothesize that the above mentioned unusual EPR low-field features are due to formation of O-_Cu2+_O- (S=3/2) systems, in which O- ions interact with Cu2+ ions. Then the latter become no more available as catalytic centres for the reaction.